POLYMERS

POLYMERS

1. Uses of polymers

   • Poly(phenylethene)/Polystyrene: Used in foam packaging, insulation, model-making. Biodegradable materials replacing polystyrene.
   • Poly(propene): food packaging, dishwasher safe containers, carpet fibres. Resistant to chemical attack.
   • Poly(ethene): most widely-used plastic.

2. Polymer Waste

   • Polymers are 10% of our waste, landfill filling up quickly.
   • Only a tiny amount is being recycled.
   • Need to be recycled, but contain additives containing poisonous heavy metal ions.
   • New legislation may restrict the use of polymers in packaging

3. Recycling Polymers

   • Sorting
     • Optical scanning to separate PET from HDPE, PVC from other plastics.
     • If there is any PVC in the PET then it is unsuitable for re-use.
   • Reclamation
     • Mechanically chopped into small flakes then washed. Melt pellets then remould them.
     • PET: From bottles to carpets, clothing, other bottles
     • HDPE: To make hard plastics.
     • LDPE: To make plastic bags.

4. Fuel Source

   • Burning, produces heat energy, harnessed to make electricity. Poly(ethene) used to cover crops in growing season.
   • Burns old, rubber-based tyres to generate electricity, removes unsightly tyres from the environment

5. Feedstock recycling

   • Convert polymers into synthesis gas, mixture of hydrogen and carbon monoxide.
   • Hydrocarbons and synthesis gas used as chemical feedstock for conversion into useful products.

6. Recycling PVC

   • PVC problematic due to high content of chlorine.
     • Uneconomical, recycling costs more than production from crude oil.
     • Incineration releases toxic fumes, cause corrosion in the plant.
   • First commercial recycling plant. Separated by other scrap by dissolving in solvents. Recovered by precipitation.

7. Biodegradable and compostable polymers

   • Made from starch, maize, cellulose and lactic acid.
   • Break down as a result of bacterial activity.
   • Must break down into Carbon dioxide, water, inorganic compounds and biomass.
   • Biobags made from cornstarch, bag and waste composted together.